My research is focused on
understanding the evolution of surfaces and near surfaces of the Earth and other planets,
including lakes on Titan, landslides on Mars and icy satellites as well as
aeolian transport on Mars, Venus and Titan.
Other planets allow us to test our understanding of geological
and climate processes under a wide range of conditions.
By combining observations from planetary
exploration missions with image processing and numerical modeling, I try to understand
what controls the evolution of continental surfaces (including planetary counterparts) and more specifically mass wasting, aeolian and hydrology processes.

Friction Weakening of Landslides
One of the ultimate goals in landslides hazard assessment is
to predict their runout distance
and velocity. Despite the great amount of work already devoted to this
issue, main questions are still unresolved on the physical processes at work
in these granular flows at the natural scale. Analytical and numerical models of granular flow over sloping beds are
combined with observations from field surveys and remote-sensing to
investigate the cause of mean friction softening with increasing
volume.

Scar geometry and topography effects on landslides dynamics
The impact of the initial scar geometry on flow and distribution of the
deposits is studied here using satellite data and numerical modeling of theoretical landslides,
and Martian landslides informed by geomorphological analysis, by varying the initial scar
geometry from spoon‐shaped to steep wall geometry. Our results show that the runout
distance is a very robust parameter that is only slightly affected by the change in the
geometry of the initial scar. On the contrary, the lateral extent of the deposit is shown to be
controlled by the scar geometry, providing unique insights into the initial landsliding
conditions on Mars and makes it possible to accurately recover the volume initially involved,
an essential ingredient for volume balance calculation.

Clues to Titan Hydrology from Enhanced SAR Image Processing
As on Earth and ancient Mars, Titan is known to possess
an active hydrologic cycle, including lacustrine/marine,
fluvial and pluvial processes. Although isolated small lakes may be fed by atmospheric volatiles and
subsurface ﬂow, larger seas with associated channel networks require surface runoff, and thus offer analogues to
terrestrial drainage systems. The Cassini RADAR operating in SAR mode imaged fluvial networks with tributaries merging and draining into lakes and seas. In order
to quantify the interactions of fluvial/lacustrine/marine
processes with the topography we have obtained from stereo using a de-speckling pipeline, new insights
based on an adapted algorithm for de-noising images using an appropriate multiplicative noise model. The
data reveals details of the valleys incised into the terrain, shoreline morphology, and contrast variations in the
dark, liquid covered areas, previously difficult to detect.
The latter are suggestive of submerged valleys and gradients in the bathymetry.

Pacing Early Mars fluvial activity at Aeolis Dorsa
The impactor flux early in Mars history was much higher than today, so sedimentary sequences include many buried craters. In combination with models for the impactor flux, observations of the number of buried craters can constrain sedimentation rates. Using the frequency of crater-river interactions, we find net sedimentation rate 20-300 microns/yr at Aeolis Dorsa. This sets a lower bound of 1-15 Myr on the total interval spanned by fluvial activity around the Noachian-Hesperian transition. We predict that Gale Crater's mound (Aeolis Mons) took at least 10-100 Myr to accumulate, which is testable by the Mars Science Laboratory.

Insights on genetic links between outflows and chasmata: Example of Ganges
Within the Valles Marineris region on Mars, systems of interconnected valleys interpreted as flood channels reveals the presence
of braided channels and strong incisions into the bedrock. These channels can be used to probe the
relationship between the formation of Chasmata and outflow channels. We shown that outflows predated the opening of Chasmata. In addition, possible sapping valleys were formed at the
mouth indicating that a residual aquifer could have been responsible for a late hydrogeological activity after the opening
and the widening of Chasmata.

Quantitative analysis of Sand Fluxes on Mars
Wind is the major agent of sediment transport on Mars. A quantitative
estimate of aeolian processes is therefore essential to assess recent geological
evolution and current climate. Here, I contributed to Bridges et al., Nature (2012) where we derived sand flux, the key quantity that
controls the style and rate of landscape evolution. By determining the migration rate
of ripples on the surfaces of Martian dunes, we show that the dunes are near steady
state. Dune migration rate varies inversely with size and position within the dune
field.